Veronica VGA board finalized

The latest update in the Veronica 6502 computer project is this finalized VGA board which now has a home in the machine’s backplane.

We’ve been glued to the updates [Quinn Dunki] has been posting about the project for many months now. Getting the GPU working proved to take quite a bit of time, but we learned a ton just by following along. The video output had humble beginnings way back in March. That breadboarded circuit got complicated very quickly and that was before it was even interfaced with the CPU. As you can see from the image above, etching and populating the GPU board really cleans up the build. We’re sure it’s robust enough to move around at this point. We wonder if she’s planning on showing it off at a Maker Faire or another geeky gathering?

It really has become clear how wise [Quinn] was to design a backplane board early on. It plays right into the modular concept. She was even smart enough to include that SIL pin header on the near side of the board which was used heavily while prototyping this video module.

The TI99 didn’t rule much, unfortunately. Didn’t it run at less than 1MHz? And rather stupidly had all the RAM connected to the hungry video controller, with just 256 bytes (I looked it up!) connected directly to the CPU by way of apology. So all real RAM storage was in whatever of the 16K the video chip wasn’t using,accessed a byte at a time through an IO port. The CPU’s registers, too, were in RAM (except PC and a couple of other special-purpose ones).

So a 3MHz 16-bit computer was sort-of a heap of crap. How you can make so many WRONG decisions in designing a little home computer is astounding! Atari’s range of the same time came about from their arcade expertise. Commodore was a real home computer, designed to be good for games by enthusiatic experts. And the Sinclair machines were designed to get as much functionality out of almost nothing as was possible!

Commodore disk drives had an entire 6502 processor (or even a pair!) with RAM and ROM just to run it, through a serial port. The Sinclair Spectrum’s microdrives were reels of whizzing tape, like tiny 8-tracks, where the spool motor, read / write head, and whatever were driven directly from the CPU, using bits from a byte bashed out in real-time. Then read in the same way. All using one of the Z80’s IO ports. Which weren’t even decoded fully! From the bottom 8 bits of the address bus, one line at a time could be low. That, and MEM/IO at the same time, drove each piece of hardware. Bit 0 for the keyboard / beeper / tape drive / screen border. Bit 1 for the printer, bit 4(?) for the microdrive and serial port, etc.

Serial port, too, bit-bashed. A network port, a different bit of the same byte the serial port was bashed from.

The printer was a spring-clip on a belt. As it whizzed past, an encoder on it’s drive shaft told the computer’s Z80 where it was. Sending voltage to it made a spark from the pointy end of the clip, to the metal-coated paper, and burned away the aluminium to reveal the black paper underneat!

The whole thing, network, serial, 8 microdrives, sound and whatever I’ve forgotten… all driven by the Z80 CPU directly in realtime using partial decoding of the address lines!

A Z80, some ROM and RAM, and a ULA did it all! Apart from a couple of 7400-series chips and a transistor or two. Hi-res colour too. The add-on Interface 1 provided the microdrive / serial / network port. Again, just another ULA connected onto the Spectrum’s single expansion port. an edge connector with the full Z80 bus and a couple of other pins from the ULA. Cost next to nothing, weighed nothing, and brought millions of kids their first computer! Was one of the best selling computers in Britain at least, and probably the main reason so many games software houses are British. Half of them date back to the Spectrum, the other half just employ people who do!

Anyway… yeah… From a chip-stuffed overblown toaster, to the same amount of function and utility using bit-banging and a bit of sticky tape. Interesting how the British did it so much differently. Sinclair himself had made his career out of selling low-price miniaturised consumer goods though, to him computers were just another business. I think the American side had a lot of designers who started off with mainframes, not pocket radios and cheap hifi.

Is anyone interested in converting a photo display into a computer monitor? A photo display is a LCD monitor with a built-in computer. Theoretically, it should be possible to convert to a monitor by removing parts rather than adding.